Control system



P .15, 1952 J. R. BOYKIN 2,611,091

CONTROL SYSTEM Filed June 30, 1944 INDUCTION HEATING DEVICE wmuzssss; INVENTOR AIM/5M John A! 50 1410.

WQ- W BY Patented Sept. 16, y 1952 UNITED STATES PATENT OFFICE CONTROL SYSTEM John R. Boykin, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 30, 1944, Serial No. 542,981

'1 Claim. 1

My invention relates to oscillation generator systems and in particular relates to such systems employing electrical discharge tubes and in which it is desirable to be able to adjust the value of the power output over substantial range.

Oscillation generators of the electrical discharge tube type generally employing tunable circuits can have the value of their power output regulated to a desired value, in accordance with methods now prevalent in the art, either by (l) varying the filamentvoltage, (2) tuning the load circuit, or (3) changing taps on an output transformer or coil. Methods (1) and (2) are, however, limited in'the range of variation which can be produced under practical circumstances by their employment, and method (3) only permits variations in steps of substantial magnitude rather than by continuous variation.

It is accordingly one object of my invention to provide an oscillation generator, to be employed, for example,- in induction heating service, of which the magnitude of power output may be varied gradually over a wide range.

It is another object of my invention to provide an oscillation generator system in which the power output may be varied over a very substantial range and which shall be low in first cost.

It is a still further object of my invention to provide an oscillation generator system in which the output power may be varied by substantially infinitesimal steps over a wide range and which shall require only relatively small and compact control elements for this purpose.

It is still another object of my invention to produce an oscillation generator system for supplying power in which the magnitude of the output power may be gradually varied over a wide range without substantially varying the output frequency.

Still another object of my invention is to provide an oscillation generator system particularly adapted for use in the induction heating field in which the power output may be varied at will over a wide range gradually and without the intervention of steps of finite magnitude.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawing in which the single figure is a schematic diagram of the circuits of an oscillation generator and its control means embodying the principles of my invention.

Referring in detail to the drawing, an oscillation generator I, which may be of any suitable type conventional in the art comprising an electrical discharge tube having a control electrode, has its plate circuit fed from the positive terminal 2 of a source of high voltage through the primary 3 of an output transformer having a secondary winding 4 adapted to connect to any desired load such, for example, as an induction heating device. A winding 5 connected between the control electrode and the cathode of the tube 1 through a capacitor 6 is inductively related to the primary winding 3 and is shunted by a capacitor 1. A capacitor 10 shunts the primary winding 3. The cathode of tube l is connected to the negative terminal of the source 2 by way of ground. The arrangement so far discussed will be recognized as a conventional type of oscillation generator circuit.

In the prior art such an oscillation generator has customarily been operated with output power continuously flowing throughout the period in which it is desired to heat the load or otherwise supply it with power. In contrast to this, in accordance with my invention I impress on the control electrode of the tube I a control voltage consisting of substantially square-topped waves separated from each other by intervals in which the voltage of the control electrode falls to such a low value that the tube I is no longer able to continue in oscillation and its power output falls to zero. These voltage pulses are derived from the control tubes 8 and 9 by way of the keying tube H, all of which I am about to describe in detail. By varying the relative length of the square-topped voltage pulse above mentioned to the intervals of zero voltage intervening between them, it is possible to vary the fraction of the time during which the generator I supplies substantial power to the load connected to output winding 4 over substantially any desired range, and correspondingly to vary the power supplied to the load through winding 4 from zero to 10 0% of the maximum power which the tube 1 is capable of generating. Since the periodicity of the square-topped pulses above mentioned can be made to have substantially any value over a wide range, the switching on and off of power from the oscillator I may take place with a high degree of rapidity. Furthermore, the ratio of the width oi the square-topped pulse to the intervals between pulses may be varied with practically infinitesimal gradations, so that it is correspondingly possible to vary the power output of the generator I in substantially infinitesimal amounts.

Referring in detail to tubes 8 and 9, the former has its anode fed from the positive terminal 12 of a suitable direct-current source through a resistor I3. The tube 9 may be fed from the same source through a resistor [4, the negative terminal of the source being grounded. The cathodes of the tubes 8 and 9 are connected together and grounded through a resistor I5. The cathode of the tube 9 is likewise connected to the positive terminal I2 through a; resistor 16. The control electrode of tube 8 is connected through a capacitor l 7 to the anode of the tube 9, and the control electrode of the tube 9 is connected to the anode of the tube 8 through a capacitor [8. A resistor It is connected between the grid of the tube 8 and the grid of the tube 9, and is provided with a slidable contact 2| which is connected to ground.

The above-described circuit connections forthe tubes 8 and 9 make them act-as a generator of square-topped periodic waves separated from each other by intervals of substantial zero voltage and the fraction of the wave period over which the square voltage pulse'extends can be varied at will by moving the contact 2.! along the-resistor 1 9.

While I have described the resistor 19 and variable top 21 as a specific means for varying the fraction or the wave period over which the square voltagepulse extends, it should be recognized that any alternative method :of varying the ratio'of the efiective resistances between the ground and the control electrodes of tubes 8 and rQ-maybe-substituted therefor. l

Theanode of the tubeei's connected to the control electrodebfa'keyingtube1il of which the anode is connected tel-ground. The cathode of the tube H is connected through a.resistorz22 to its control electrode and is likewise connected through a resistor 23;to theicommon terminal of the capacitors 6 and v1. .As a result of this arrangement, positive voltage pulses are impressed through, the tube-H at intervals on the control electrode of the tube "1, andcause-the latter to produceoscillations and-supply powertothe load connected to the terminals: of winding 4 as -;long as the positive voltage pulse lasts. 'I fhereafter the voltage impressed 'by the keying tube ill ,on the electrode of tube -I falls to sucha low .valuegas-to cause the oscillation generator :I :to -,-go out of oscillation and V to q cease ,to supply substantial powerto the loadconnectedrto winding 4. This condition continues to the end tof the period of the pulse generators, 9 'whereupon'the generation :ofanewpositive pulse by the latter sets the:os

4 cillator I into oscillation again and the above described cycle is repeated indefinitely at the periodicity of the pulse generator 8, 9.

While I have described a particular form of pulse generator for impressing the square-topped voltage waves on the control load of tube I, it will be recognized that any known arrangement for impulsing such square-topped pulses may be substituted therefor.

I claim as my invention:

In combination with an electrical discharge tube having an anode circuit, a control electrode circuit comprising an impedance in series with means coasting with said anode circuit to cause said tube to. generate electrical oscillations, a

genera'torof square-topped waves, a pair of resistorsseriallyconnected between the end of said impedance remote from the cathode of said electrical discharge tube and a point on the output circuit of said generator of square-topped waves, a :second electrical discharge tube having an node; a c t ean aontr l e ectr de. a s neetion between the last mentioned control electrode and said point; a connection between the cathode of said second electrical di charge tube and the common junction of said two resistors, and -a connection :from the cathode of the first- :rnentionedelectrical discharge tube and the anode .of said second electriqal discharge tube, and toa variable tap on the output circuit of said generator of square-topped waves.

1 NRiBQYKIN- REFERENCES CITED The following references are of record in the file of this patent:

"UNITED STATES "PATENTS 

